Currently thin film processes typically require a high temperature step to form a high quality and relatively defect free phase. Indeed, the crystallization process of a material usually requires rather high temperature. However, for thin films on a substrate the interactions with the substrate are a limiting factor as diffusion must be avoided as much as possible. Often it is impossible to reconcile these different requirements. For instance for the growth of materials on polymer substrates it is clear that the maximum growth temperatures cannot exceed the glass transition temperature of the polymer. Also, for the growth of oxide films on typical semiconductor substrates, the formation of intermediary phases such as SiO2 on Si cannot be avoided if the substrate temperature becomes too high.
To circumvent these issues, a number of processes have been developed in the art such as the rapid thermal annealing process that anneal the film in a short time after the film growth. However, heating and subsequent cooling of the substrate and the thin film still cause diffusion damage.
Another method currently used in the art is to apply a “direct” or a “remote” plasma to the growing front. This plasma is usually created by a DC, RF, Microwave or ECR type of discharge whereby a whole range of active species is created such as atomic elements, excited atoms and molecules as well as electrons and different ions. When they bombard the surface, inevitably this will also lead to a heating of the substrate surface layer or the thin film growing layer. However, the energetic spectral distribution of these species is usually very large mostly including sputtering of surface atoms, which is not gentile nor electrically neutral.
The main shortcomings in the state of the art are twofold. On the one hand, since the thermal budget during the film formation on a substrate is limited, it is impossible to make a film of a good structural quality. This will limit the overall performance of the said thin film on all fronts. The second main shortcoming is related to the diffusion issues and the large set of “complicated” defects that arise as a consequence. For instance in the case of the gate stack, the diffusion of semiconductor atoms (from Si, Ge, GaAs or InGaAs) into the oxide always leads to poor electrical behavior. Vice versa, the diffusion of metallic, nitrogen or oxide species into the semiconductor also gives rise to unwanted defects into the semiconductor.
Therefore there is a need for more gentle methods and tools to grow, etch and/or anneal thin films.